I for one am not a believer in the "more versatility" argument since I re-load. Sure, you can shoot three different cartridges, but why? If you are a re-loader, all that means is that you can shoot three different *lengths* of cartridge, since you can download the 460 to 45LC levels if for some reason you would want to do that. 45LC brass might be a little cheaper than 460, but that difference would be minor in the whole scheme of things.
An analogous situation would be the .38/.357. I used to shoot both in the same revolver, but rarely do any more. Shooting a couple cylinders of 38 will quickly foul the cylinder to the point that .357 cartridges won't fit any more. It takes a serious scrubbing to get the carbon ring out so you can get .357s in again. I don't see why the 460 would be any different. Shooting .357 first negates this problem of course. Since I re-load, I just load .357 cases to .38 levels and do away with the problem all together. There are 500 Special cartridges available now, but I have absolutely no interest in them for the above reason.
Another issue is point of aim. For a handgun with the range of the 460 and 500, some type of optics are almost essential to get the most out of it. This will have to be zeroed for the load of your choice, which will of course will be a different zero for the other loads. You can mess with the scope settings while shooting, but for the recoil these things generate, I like to leave it alone to the greatest extent possible. I have a reduced load for the 500Mag for practice, and I have to use targets at a much shorter range to keep the point of impact anywhere near the point of aim. For long distance, I have to go back to the full-house loads.
Yet another issue is barrel life. The 460 runs at a much higher pressure (65,000 psi vs 50,000 on the 500Mag if I recall correctly). I have seen several posts by people bent out of shape because their 460 starts shooting poorly and they find out that S&W estimates the barrel life at around 1500 rounds. I would be bent out of shape too. For $100 or so they will put a new barrel on it if you send it back to the factory. I haven't confirmed this with S&W, by the way, so take it with a grain of salt. I have never heard of anyone wearing out the barrel of a 500Mag, but that is not to say it can't be done.
One of the reasons I got into re-loading is that I wanted to create a set of loads for my 30-30 that I could use for a variety of purposes. I figured a 100gr Plinker for practice, the 110gr HP for varmints, the 130gr HP for coyotes, the 150gr FP for small deer, and if necessary a 170gr FP for deer as well. That way I could just drop in whatever cartridge I needed at the moment. I would have the ultimate multi-purpose hunting rifle. That was the plan anyway. I quickly found that the rifle had a pronounced preference for heavier bullets. I could get the 170gr loads under 1" at 100yds off the bench. The 150s opened up a bit, and it went down hill from there. The 100gr hit a paper plate about half the time at 100 yds. So in the end I have a rifle that shoots 170gr deer loads really well, and that is all I use it for. I have no direct experience with the 460 in this regard (maybe someone else on this forum does) but it was undoubtedly optimized for the screaming velocities of the 460, and that may negatively affect accuracy on the slower 454 and 45LC loads. You could ask around about that one I guess.
I really like my 500, and don't plan on getting a 460. If the 460 had come out first I would probably have one of those and wouldn't plan on getting the 500. Six of one, half dozen of the other. I'm sure you would be happy with either one.